mx5: Define a common get_board_rev()

When booting a FSL kernel based on 2.6.35 it is necessary to pass the revision
tag to the kernel.

Place a common weak function into soc.c for such purpose.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Marek Vasut <marex@denx.de>

arch/arm/cpu/armv7/mx5/soc.c

@@ -72,6 +72,13 @@ u32 get_cpu_rev(void)
 	return system_rev;
 }
 
+#ifdef CONFIG_REVISION_TAG
+u32 __weak get_board_rev(void)
+{
+	return get_cpu_rev();
+}
+#endif
+
 #ifndef CONFIG_SYS_DCACHE_OFF
 void enable_caches(void)
 {